#include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<n;i++)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
template<typename T,typename U> inline void chmax(T &x,U y){ if(y>x) x = y; }
template<typename T,typename U> inline void chmin(T &x,U y){ if(y<x) x = y; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
inline long long max(int a,long long b){
    if(a>b) return a;
    else return b;
}
inline long long max(long long a,int b){
    if(a>b) return a;
    else return b;
}
/*}}}*/

int main(){
    int n;
    cin >> n;
    vector<ll> b(n);
    rep(i,n) cin >> b[i];

    // fi <= se
    vector<pll> a(n+1,pll(-1,-1));
    a[0].fi = 1;
    a[0].se = b[0] - 1;
    if(a[0].fi > a[0].se){
        cout << -1 << endl;
        return 0;
    }
    for(int i=0;i<n;i++){
        ll low , high;
        if(i%2==0){
            //cerr << "even" << endl;
            low = b[i] - a[i].se;
            high = b[i] - a[i].fi;
        }else{
            //cerr << "odd" << endl;
            low = a[i].fi - b[i];
            high = a[i].se - b[i];
        }
        low = max(1ll,low);
        if(low > high){
            //cerr << i << endl;
            //rep(j,i+1){
            //    cerr << a[j] << endl;
            //}
            //cerr << low << " "<< high << endl;
            cout << -1 << endl;
            return 0;
        }
        //cerr << i+1 << " -- (" << low << "," << high << ")" << endl;
        a[i+1].fi = low;
        a[i+1].se = high;
    }

    vector<ll> ans(n+1);
    ans[n] = a[n].fi;

    for(int i=n-1;i>=0;i--){
        if(i%2==0) ans[i] = b[i] - ans[i+1];
        else ans[i] = b[i] + ans[i+1];
    }

    cout << n+1 << endl;
    rep(i,n+1) cout << ans[i] << endl;
}